Exhaust-gas-turbine casing

ABSTRACT

The exhaust-gas turbine comprises a turbine casing, a shaft rotatably mounted in a bearing housing, a turbine wheel arranged on the shaft, and a heat-protection wall, the heat-protection wall defining with the turbine casing an inflow passage leading to the turbine wheel. The heat-protection wall has two seatings, the first seating resting on the bearing housing and the second seating resting on the turbine casing. 
     If the heat-protection wall becomes hot, the two seatings are pressed against the bearing housing and the turbine casing. The turbine casing is pressed outward in the radial direction. Centering of the heat-protection wall and thus also of the turbine casing is ensured by the radially inner seating of the heat-protection wall.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of exhaust-gas-operatedturbochargers. It relates to an exhaust-gas turbine, in particular abearing housing, a turbine casing, and a heat-protection wall of anexhaust-gas turbine, the heat-protection wall, in the exhaust-gasturbine, defining with the turbine casing an inflow passage leading tothe turbine wheel, the turbine wheel being arranged on a shaft rotatablymounted in the bearing housing.

2. Discussion of Background

Exhaust-gas turbochargers are used for increasing the output of internalcombustion engines. Turbochargers having a turbine wheel subjected toradial flow and an inner bearing arrangement of the shaft to which theturbine wheel is attached are mainly used in the low output range up toa few megawatts.

In uncooled exhaust-gas turbochargers, in which the gas-conductingpassages are not cooled, the exhaust-gas temperature at the turbineinlet is higher, as a result of which the thermal efficiency of themachine and the output delivered to the air compressor per exhaust-gasquantity increase.

The uncooled gas-inlet or turbine casing, which has a temperature of,for example, 650° C. during operation, is usually fastened directly tothe bearing housing, which at 150° C., for example, is substantiallycooler. In certain fields of application, the bearing housing, incontrast to the gas-conducting passages, is cooled to the aforesaidtemperature. In addition, as described in EP 0 856 639, an intermediatewall serving as heat protection may be arranged in the region of aninflow passage leading to the turbine wheel, this intermediate wallshielding the bearing housing from the hot gas conducted in the inflowpassage. In this case, the intermediate wall may be arranged such as tobe separated from the bearing housing by an appropriate air orcooling-liquid zone and may have only a few, defined contact points inorder to avoid as far as possible corresponding heat bridges to thebearing housing.

In conventional exhaust-gas turbines, straps or “profiled-clampconnections” or “V-band connections” are used in order to fasten theturbine casing to the bearing housing. In order to achieve as high anefficiency as possible, the air gap between the turbine blades and theturbine casing is to be kept as small as possible. However, thisrequires this casing wall and the turbine wheel to be centered relativeto one another at all times, in particular during operation under fullload and during corresponding thermal loading of all parts. Since thecentering seat of the turbine casing relative to the bearing housingsometimes widens radially as a result of the large temperaturedifference between the bearing housing and the turbine casing, theturbine casing may become offset relative to the bearing housing and inparticular relative to the turbine shaft mounted therein, i.e. theturbine casing is no longer centered in the radial direction relative tothe shaft and the turbine wheel arranged thereon. Such an offset, whichmay be additionally encouraged by external actions of force, leads tocontact between the turbine blade tips and the casing wall of theturbine casing, to corresponding abrasion or defects and, associatedtherewith, to considerable losses in efficiency of the exhaust-gasturbine.

EP 0 118 051 shows how an offset of the hotter component can be avoidedby means of groove/ridge connections arranged in a star shape andmovable in the radial direction.

This conventional, but relatively costly, solution approach, in whichthe production process, in addition to pure turning operations, alsoincludes milling operations, only permits a restricted number ofdifferent casing positions on account of the discrete number ofgroove/ridge connections. However, a solution approach in which theposition of the turbine casing relative to the bearing housing can beset in an essentially infinitely variable manner is desirable.

SUMMARY OF THE INVENTION

Accordingly, one object of the invention is to provide a novelexhaust-gas turbine of the type mentioned at the beginning which permitsan improvement in the turbine efficiency by centering the turbine casingrelative to the shaft mounted in the bearing housing.

According to the invention, this object is achieved by thecharacterizing features of patent claims 1, 7 and 12 and by patent claim16.

The advantages achieved by the invention may be seen in the fact thatthe centering of the turbine casing relative to the shaft mounted in thebearing housing can be ensured without additional components. Thebearing housing, turbine casing and heat-protection wall only needslight additional machining. As a result, no substantial additionalcosts arise for the exhaust-gas turbine.

The position of the turbine casing relative to the bearing housing canbe set in an infinitely variable manner, since according to theinvention there is no positive-locking connection between the bearinghousing and the turbine casing.

This type of centering is suitable for all common types of connectionbetween bearing housing and turbine casing, since, according to theinvention, the centering is effected by components in the interior ofthe turbine casing.

Further advantages follow from the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows a schematic view of a first exemplary embodiment of theexhaust-gas turbocharger according to the invention,

FIG. 2 shows an enlarged view of the exhaust-gas turbocharger accordingto FIG. 1,

FIG. 3 shows a schematic view of a second exemplary embodiment of theexhaust-gas turbocharger according to the invention,

FIG. 4 shows a schematic view IV-IV from FIG. 3,

FIG. 5 shows a schematic view of a third exemplary embodiment of theexhaust-gas turbocharger according to the invention, and

FIG. 6 shows a schematic view VI-VI from FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, theexhaust-gas turbocharger mainly comprises a compressor (not shown) andan exhaust-gas turbine schematically shown as a radial-flow turbine inFIG. 1. The exhaust-gas turbine mainly comprises a turbine casing 1,having a radially outer, spiral gas-inlet casing and a casing wall 12 onthe gas outlet side, a bearing housing 4 having a shaft 3 rotatablymounted by means of bearings 31, and a turbine wheel 5 arranged on theshaft and having moving blades 51. On the compressor side, a compressorwheel (likewise not shown) is arranged on the shaft.

The gas-inlet casing merges downstream in the direction of the arrowinto an inflow passage 6 for the exhaust gases of an internal combustionengine (likewise not shown) connected to the exhaust-gas turbocharger.The inflow passage is defined on one side by the casing wall 12 on thegas outlet side, whereas a disk-shaped intermediate wall 2 serving asheat protection is arranged on the other side. The heat-protection wall,which at least partly defines the inflow passage on the side of thebearing housing and/or is arranged at least partly in the axialdirection between turbine wheel and bearing housing, shields the bearinghousing lying behind it from the hot exhaust gases.

Furthermore, a nozzle ring 7 is arranged in the inflow passage betweenthe heat-protection wall and the casing wall 12 on the gas outlet side.

The turbine casing 1 is secured to the bearing housing 4 by means ofstraps 43 in the embodiment shown, the straps, which are secured to theturbine casing with screws 42, permitting certain movements of theturbine casing relative to the bearing housing 4 in the radialdirection. As can be seen from the figure, by the straps 43 beingscrewed tight, the heat-protection wall 2 and the nozzle ring 7 areclamped in place between turbine casing 1 and bearing housing 4 and areaccordingly fixed in the axial direction. In the stationary state of theexhaust-gas turbine, when turbine casing and bearing housing are cold,the turbine casing rests on the bearing housing and is thus accordinglycentered relative to the shaft and the turbine wheel arranged thereon.

In the first embodiment, shown enlarged in FIG. 2, of the exhaust-gasturbine according to the invention, a seating 21 designed as anencircling edge is arranged on the heat-protection wall 2 in theradially inner region and rests on a seating 41, likewise designed as anencircling edge, of the bearing housing. In the stationary state of theexhaust-gas turbine, when the heat-protection wall is also cold inaddition to the bearing housing, there may be in each case a small airgap of a few micrometers up to several hundred micrometers between thetwo seatings, a factor which in particular permits simple fitting, i.e.the slipping of the heat-protection wall onto the bearing housing in theaxial direction. In the radially outer region, the heat-protection wallis disposed with a radially outer seating 22 on a seating 11, directedradially inward, of the turbine casing, there likewise being acorresponding, small air gap between the two seatings in the stationarystate of the exhaust-gas turbine.

In the operating state of the exhaust-gas turbine, when theheat-protection wall has a considerably higher temperature compared withthe bearing housing, the heat-protection wall expands in a thermallyinduced manner, in particular in the radial direction. The two air gapsare reduced, in the course of which, in particular, the inner seating 21of the heat-protection wall is pressed with great force against thecorresponding seatings 41 of the cool bearing housing. The air gapbetween the outer seating 22 of the heat-protection wall and the seating11 of the turbine casing can as a rule only be reduced, but notcompletely closed, since the turbine casing likewise expands on accountof the considerable heat. Due to the radially inner seating 21 of theheat-protection wall, which bears against the seating 41 of the bearinghousing, accurate centering of the heat-protection wall 2 is ensured,and accurate centering of the turbine casing 1 is also ensured thanks tothe reduced outer air gap.

If a material having a higher coefficient of thermal expansion than thematerial of the turbine casing is selected for the heat-protection wall,the heat-protection wall expands to a greater degree than the turbinecasing and presses the latter outward in the radial direction. Thisadditionally improves the centering of the turbine casing relative tothe heat-protection wall.

FIG. 3 and FIG. 4 show a second embodiment of the exhaust-gas turbineaccording to the invention. A seating 21 designed as an encircling edgeis again arranged in the radially inner region and again rests on aseating 41, likewise designed as an encircling edge, of the bearinghousing. In addition to or as an alternative to the simple seating 22 inthe radially outer region of the heat-protection wall 2, centering lugs23 are provided, these centering lugs 23 being arranged in a distributedmanner along the circumference of the heat-protection wall. Thesecentering lugs 23 engage in corresponding slots 15 in the turbinecasing, thereby resulting in radial guidance of the turbine casing 1relative to the heat-protection wall 2. In the stationary state of theexhaust-gas turbine, there are corresponding air gaps in particular inthe region of the inner seatings, a factor which again permits simplefitting of the heat-protection wall. In this case, the heat-protectionwall 2 appropriately oriented on account of the centering lugs 23 ispushed into the turbine casing 1 in the axial direction. In theoperating state, the heat-protection wall again expands in the radialdirection. The air gap is closed and the seating 21 of theheat-protection wall is pressed against the corresponding seating 41 ofthe bearing housing and accordingly centered. In the radially outerregion, the centering of the turbine casing 1 is ensured by thecentering lugs 23 guided in the slots 15.

Alternatively, the centering lugs may be arranged on the side of theturbine casing and the corresponding slots may be set into theheat-protection wall. Or slots may be set into both the turbine casingand the heat-protection wall, into which slots connecting wedges orplugs are pushed in the axial direction.

This second embodiment is suitable in particular in the case of veryhigh temperatures of the turbine casing, since, owing to the radiallydirected slots and the centering lugs guided therein, centering of theturbine casing relative to the heat-protection wall is ensuredirrespective of the thermally induced expansion of the turbine casing.

Despite this positive-locking connection between turbine casing andheat-protection wall, the position of the turbine casing relative to thebearing housing can be set in an infinitely variable manner, since thereis no positive-locking connection between the heat-protection wall andthe bearing housing and thus there is also no positive-lockingconnection between the turbine casing and the bearing housing.

FIG. 5 and FIG. 6 show a third embodiment, slightly modified comparedwith the second embodiment, of the exhaust-gas turbine according to theinvention. The centering lugs 23 are provided in the radially innerregion of the heat-protection wall. In this case, the lugs 23 may bearranged on the heat-protection wall and engage in corresponding slots45 in the bearing housing, or lugs which engage in corresponding slotsin the heat-protection wall may be arranged on the bearing housing. Inthe latter case, the slots may be designed as through-holes or only assurface recesses in the heat-protection wall. Radial guidance of theheat-protection wall 2. relative to the bearing housing 4 is obtained.In the radially outer region, the heat-protection wall in accordancewith the first embodiment is disposed with the radially outer seating 22on the seating 11, directed radially inward, of the turbine casing,there again being a corresponding air gap in the stationary state of theexhaust-gas turbine, a factor which permits the fitting of theheat-protection wall. In this case, the heat-protection wall 2,appropriately oriented on account of the centering lugs, is pushed ontothe bearing housing 4 in the axial direction. In the operating state,the heat-protection wall again expands in the radial direction. Asdescribed above, the air gap in the outer region decreases and thereforeleads to corresponding centering of the turbine casing relative to theheat-protection wall. The expansion of the heat-protection wall canagain be intensified by the selection of a material having acorrespondingly higher coefficient of thermal expansion in order toadditionally improve the centering of the turbine casing relative to theheat-protection wall. Owing to the temperature-independent centering ofthe heat-protection wall relative to the bearing housing by thecentering lugs arranged in the inner region, this embodiment is suitablein particular for the transient operation or at low gas-inlettemperatures.

Despite the positive-locking connection between heat-protection wall andbearing housing, the position of the turbine casing relative to thebearing housing, as is already the case in the first two embodiments,can be set at any desired angle, since there is no positive-lockingconnection between the heat-protection wall and the turbine casing andthus there is also no positive-locking connection between the bearinghousing and the turbine casing.

A suitable material for the heat-protection wall of all threeembodiments would be, for example, Ni-resist, having a coefficient ofthermal expansion around 30 percent higher than cast iron.

In the radially outer region of the heat-protection wall, the seatingrelative to the turbine casing may also be effected via an intermediatepiece arranged between heat-protection wall and turbine casing, inparticular via parts of the nozzle ring arranged in the inflow passage.In this case, the nozzle ring and the heat-protection wall or parts ofthe nozzle ring and the heat-protection wall may be produced in onepiece.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A heat-protection wall for an exhaust-gas turbine, the exhaust-gasturbine having a turbine casing, a shaft rotatably mounted in a bearinghousing, and a turbine wheel arranged on the shaft, and theheat-protection wall defining with the turbine casing an inflow passageleading to the turbine wheel, wherein the heat-protection wall has atleast two seatings for centering the turbine casing relative to theshaft, a first seating of the at least two seatings being provided forresting on the bearing housing, and a second seating of the at least twoseatings being provided for resting on the turbine casing; wherein atleast one of the first or second seatings is designed as an encirclingedge which is provided for resting on the bearing housing and/or theturbine casing; wherein the first and second seatings are designed to bedirected radially outwards.
 2. An exhaust-gas turbine having a turbinecasing, a shaft rotatably mounted in a bearing housing, a turbine wheelarranged on the shaft, and a heat-protection wall as claimed in claim 1,wherein an encircling edge for resting on an encircling edge of theheat-protection wall is provided on the bearing housing and/or on theturbine casing.
 3. A heat-protection wall for an exhaust-gas turbine,the exhaust-gas turbine having a turbine casing, a shaft rotatablymounted in a bearing housing, and a turbine wheel arranged on the shaft,and the heat-protection wall defining with the turbine casing an inflowpassage leading to the turbine wheel, wherein the heat-protection wallhas at least two seatings for centering the turbine casing relative tothe shaft, a first seating of the at least two seatings being providedfor resting on the bearing housing, and a second seating of the at leasttwo seatings being provided for resting on the turbine casing; andwherein slots are set into the heat-protection wall either in the regionof the first seating or in the region of the second seating, which slotsare provided for receiving centering lugs attached either to the bearinghousing or to the turbine casing.
 4. An exhaust-gas turbine, having aturbine casing, a shaft rotatably mounted in a bearing housing, aturbine wheel arranged on the shaft, and a heat-protection wall asclaimed in claim 3, wherein the centering lugs which are provided forengaging in the slots which are set into the heat-protection wall arearranged either on the bearing housing or on the turbine casing.
 5. Abearing housing for an exhaust-gas turbine, the exhaust-gas turbinehaving a turbine casing, a shaft rotatably mounted in the bearinghousing, a turbine wheel arranged on the shaft, and a heat-protectionwall which, in the exhaust-gas turbine, defines with the turbine casingan inflow passage leading to the turbine wheel, the heat-protection wallhaving means for centering the turbine casing relative to the shaftmounted in the bearing housing; wherein the bearing housing, forcentering the turbine casing via the heat-protection wall and relativeto the shaft mounted in the bearing housing, has centering lugs whichare provided for engaging in slots which are set into theheat-protection wall.
 6. A bearing housing for an exhaust-gas turbine,the exhaust-gas turbine having a turbine casing, a shaft rotatablymounted in the bearing housing, a turbine wheel arranged on the shaft,and a heat-protection wall which, in the exhaust-gas turbine, defineswith the turbine casing an inflow passage leading to the turbine wheel,the heat-protection wall having means for centering the turbine casingrelative to the shaft mounted in the bearing housing; wherein slots areset into the bearing housing for centering the turbine casing via theheat-protection wall and relative to the shaft mounted in the bearinghousing, said slots extending radially and are provided for receivingcentering lugs attached to the heat-protection wall.
 7. A turbine casingfor an exhaust-gas turbine, the exhaust-gas turbine having a bearinghousing, a shaft rotatably mounted in the bearing housing, a turbinewheel arranged on the shaft, and a heat-protection wall which, in theexhaust-gas turbine, defines with the turbine casing an inflow passageleading to the turbine wheel, the heat-protection wall having means forcentering the turbine casing relative to the shaft mounted in thebearing housing, wherein the turbine casing, for centering the turbinecasing via the heat-protection wall and relative to the shaft mounted inthe bearing housing, has centering lugs which are provided for engagingin slots which are set into the heat-protection wall.
 8. A turbinecasing for an exhaust-gas turbine, the exhaust-gas turbine having abearing housing, a shaft rotatably mounted in the bearing housing, aturbine wheel arranged on the shaft, and a heat-protection wall which,in the exhaust-gas turbine, defines with the turbine casing an inflowpassage leading to the turbine wheel, the heat-protection wall havingmeans for centering the turbine casing relative to the shaft mounted inthe bearing housing; wherein slots are set into the turbine casing forcentering the turbine casing via the heat-protection wall and relativeto the shaft mounted in the bearing housing, said slots extendingradially and being provided for receiving centering lugs attached to theheat-protection wall.
 9. An exhaust-gas turbine having a turbine casing,a shaft rotatably mounted in a bearing housing, a turbine wheel arrangedon the shaft, and a heat-protection wall wherein the heat-protectionwall has at least two seatings for centering the turbine casing relativeto the shaft, a first seating of the at least two seatings beingprovided for resting on the bearing housing, and a second seating of theat least two seatings being provided for resting on the turbine casing,wherein the heat-protection wall has centering lugs either in the regionof the first seating or in the region of the second seating, whichcentering lugs are provided for engaging radially extending slots whichare set into either the bearing housing or the turbine casing.